In this letter, Lee DeForest promotes the reduction of interference by replacing "damped" spark-transmitters with "sustained" continuous-wave transmitters. The references to "radio" is unusual--at this time radio was still almost universally called "wireless" in the United States.
 
Electrical World, June 22, 1907, page 1270:

Interference  with  Wireless  Messages.
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To  the  Editors  of  Electrical  World:
    SIRS--The news item in your recent issue concerning the policeman's son in Washington who takes delight in churning up the ether around the Navy Yard and mocking various distant wireless stations, brings up strikingly the necessity for early legal protection of legitimate workers from such vandals. In this connection there is no wireless reform more needed, so it appears to me, than the necessity of early legislation defining, not the wave-lengths, but the maximum limit of damping of wave-trains which can be permitted in any radio-telegraph station. This factor, damping, is of far more vital import than any regulation of wave-lengths. The damped half-tuned wave is an etheric pirate, and should be prohibited, the world over. I believe the time is not far distant when the operator who sends out strongly damped vibration of even small energy will be penalized by Federal statute. Radio chaos will certainly be the result until such stringent regulation is enforced. The day of the barbarous spark discharge is numbered, and the sooner it is classed with the filings coherer the better.
    Not until then can any legislation or intelligent and skilled syntonization prevent woeful interference, however unintentional. Limit all wireless communication to the sustained oscillation methods; and there will be ample gamuts of wave-length to "go around." The bugbear of interference, and much of the discussions in international conventions will be quite unnecessary.
    Above all, the ubiquitious amateur with his high-school Ruhmkorf coil, the operator of the "brute force and ignorance" wireless school, must be eliminated. To effect this will not be so difficult as might appear at first blush. The mischievously minded "expert" cannot do much harm so long as he keeps his antenna "hidden under a bushel," and a "wireless detective" with small portable receiver can readily spot the source of annoyance by a brief scouting expedition. With the rapid spread of radio-telegraphy and telephony legislation and policing will soon be in public demand.
    NEW YORK CITY.LEE DE FOREST.